Dynamics of the penA gene in serogroup C meningococcal strains

Haemophilus influenzae and Haemophilus haemolyticus in tonsillar cultures of adults with acute pharyngotonsillitis

OBJECTIVE

The aim of this study was to evaluate the clinical implication of Haemophilus haemolyticus, one of the closest relative of Haemophilus influenzae, on acute pharyngotonsillitis.

METHODS

We applied polymerase chain reaction (PCR) for 16S ribosomal DNA (rDNA) and IgA protease gene (iga) to distinguish H. haemolyticus and H. influenzae.

RESULTS

Among the 199 Haemophilus spp. isolated from 214 patients with acute pharyngotonsillitis, 52 (24.3%) H. influenzae strains and 23 (10.7%) H. haemolyticus strains were identified by polymerase chain reaction (PCR) for 16S rDNA and IgA protease gene (iga). All H. haemolyticus strains showed hemolysis on horse blood agar and there were no other Haemophilus spp., nonhemolytic H. haemolyticus and H. influenzae variant strains that had absent iga gene. H. hemolyticus showed close genetic relationship with H. influenzae evaluated by pulsed field gel electrophoresis (PFGE). The cases of acute pharyngotonsillitis showing WBC=7000/mm(3) or CRP=8 mg/dl were frequently found among cases with H. influenzae rather than cases with H. haemolyticus.

CONCLUSION

H. haemolyticus is a pharyngeal commensal that is isolated frequently from adults with acute pharyngotonsillitis.

The modular architecture of meningococcal factor H-binding protein

Meningococcal factor H binding protein (fHbp) is a promising vaccine antigen that binds the human complement downregulatory molecule factor H (fH), and this binding enhances the survival of the organism in serum. Based on sequence variability of the entire protein, fHbp has been divided into three variant groups or two subfamilies. Here, we present evidence based on phylogenetic analysis of 70 unique fHbp amino acid sequences that the molecular architecture is modular. From sequences of natural chimeras we identified blocks of two to five invariant residues that flanked five modular variable segments. Although overall, 46 % of the fHbp amino acids were invariant, based on a crystal structure, the invariant blocks that flanked the modular variable segments clustered on the membrane surface containing the amino-terminal lipid anchor, while the remaining invariant residues were located throughout the protein. Each of the five modular variable segments could be classified into one of two types, designated alpha or beta, based on homology with segments encoded by variant 1 or 3 fHbp genes, respectively. Forty of the fHbps (57 %) comprised only alpha (n=33) or beta (n=7) type segments. The remaining 30 proteins (43 %) were chimeras and could be classified into one of four modular groups. These included all 15 proteins assigned to the previously described variant 2 in subfamily A. The modular segments of one chimeric modular group had 96 % amino acid identity with those of fHbp orthologs in Neisseria gonorrhoeae. Collectively, the data suggest that recombination between Neisseria meningitidis and N. gonorrhoeae progenitors generated a family of modular, antigenically diverse meningococcal fHbps.

Evaluation of custom-made DNA microarrays for multilocus sequence typing of Neisseria meningitidis

Multilocus sequence typing (MLST) has become the gold standard for typing of a variety of bacterial and fungal micro-organisms. Others recently reported the successful use of the tiling DNA array technology to sequence-type Staphylococcus aureus. We now evaluated microarrays based on polymorphism-directed oligonucleotide design for typing of Neisseria meningitidis. The rationale behind this approach was to minimize the number of microarray probes by exploiting the comprehensive knowledge of polymorphisms combined in the Neisseria MLST website. Initial experiments using model oligonucleotides of 28-32 base-pairs in length revealed that the hybridization protocols used were highly specific. However, despite of several optimization steps, the rate of misidentification of oligonucleotides remained > 1.8% in consecutive validation experiments using arrays representing the genetic diversity at three MLST loci. We assume that the high density of polymorphic sites and the extensive GC-content variations at N. meningitidis MLST loci hinder the successful implementation of MLST microarrays based on polymorphism-directed oligonucleotide design.

Multilocus sequence typing--what is resolved?

Nucleotide sequence-based methods for bacterial typing (multilocus sequence typing; MLST) allow rapid and global comparisons between results from different laboratories. Combining this advantage with the reduced cost of high throughput sequencing, increasing automation and the amenability of sequence data for evolutionary analysis, it seems inevitable that sequence-based typing will eventually predominate over gel-based methods such as pulsed-field gel electrophoresis (PFGE) for most bacterial species. The increasing availability of multiple genome sequences for single pathogenic species, and the recent development of many new MLST schemes, means that a re-examination of the utility of multilocus sequencing, and in particular the choice of gene loci, is now appropriate.

[Multilocus sequence typing: the molecular marker of the Internet era]

Global or longer term epidemiology track the spread of clonal lineages, associated with hipervirulence or resistance or multi-resistance to antimicrobial agents. Therefore, the application of a molecular typing system for this purpose should produce data easily shared by different and geographically distant laboratories, as well as distinguish those clonal lineages even with low levels of variability accumulated in the genome.A marker based on the DNA sequence will produce objective results easily organized in data bases accessible by Internet. The application of a similar strategy that was used in the analysis of isoenzymes, by sequencing variable fragments of selected housekeeping genes, will allow obtaining a general view of the distribution of the clonal lineages and tracking their spread.

Prediction of decreased susceptibility to penicillin of Neisseria meningitidis strains by real-time PCR

Sequence analysis of the penA gene, encoding penicillin-binding protein 2 (PBP2), in 30 penicillin-intermediate (PenI) Neisseria meningitidis strains showed altered gene sequences due to the translocation of exogenous DNA blocks derived from commensal neisseriae, which are known to have PBP2 proteins with decreased affinity for the antibiotic. In order to obtain a rapid and reproducible method for predicting the PenI phenotype, a real-time PCR assay was set up with primers and probes designed on the basis of the penA gene. The A-->G mutation at codon 566, in the transpeptidase domain of the penA gene (which is present in the whole sample of 30 PenI strains and in all the 41 sequences of PenI meningococci isolated worldwide and has been deposited in the sequence databank), was chosen as a marker of penA translocations. Two hybridization probes were designed to distinguish the wild-type penA gene in penicillin-susceptible (PenS) meningococci from the mutated penA gene at codon 566 in PenI strains. Thermal analysis of probe hybridization revealed a melting temperature difference of at least 6 degrees C between PenI and PenS strains. This real-time PCR protocol characterizes the penicillin phenotype of N. meningitidis in a few hours without DNA sequencing and is useful for rapid screening of the penicillin-intermediate genotype among meningococcal isolates.

Neisseria meningitidis strains isolated from invasive infections in France (1999-2002): phenotypes and antibiotic susceptibility patterns

Infections due to Neisseria meningitidis are a major public health concern. In France, during 1999-2002, a total of 2167 clinical isolates of N. meningitidis from invasive infections were studied at the National Reference Center for Meningococci (Paris). Serogroup B strains were the most common (58%), followed by serogroup C strains (29%) and serogroup W135 strains (8%). Various phenotypes were observed, reflecting heterogeneity in the meningococcal population. Strains were susceptible to antibiotics currently used for treatment and chemoprophylaxis of meningococcal infections. However, the prevalence of meningococci with reduced susceptibility to penicillin is increasing. Such strains were heterogeneous and accounted for approximately 30% of isolates during this period, warranting continued surveillance of this phenomenon.